The present invention relates to a mass spectrometer and a method of mass spectrometry. The preferred embodiment relates to an ion guide and a method of guiding ions.
RF confined quadrupole field ion guides have proved to be an invaluable tool in many applications. The benefits of RF quadrupole ion guides relate to their ability to act as either a mass filter or a wide mass to charge ratio range ion guide with many applications requiring the ion guide to switch between these two modes of operation. In RF quadrupole ion guides of conventional design the mass to charge ratio filtering ability (resolving mode) is due to the quadrupole nature of the RF and DC fields experienced by the ions.
Inherent within these designs are pseudo-potential radial barriers that result in mass to charge ratio dependent confinement and transmission even when a large mass to charge ratio range is desired to be transmitted (i.e. in a non-resolving mode of operation). This results in what is referred to as a low mass to charge ratio (or mass) cut off and for wide mass to charge ratio range experiments results in loss of system duty cycle as the low mass to charge ratio cut off requires scanning. In addition, ions ejected from pseudo-potential wells tend to have a relatively large energy spread resulting in issues when attempting to couple such a device to a second analyser.
It is therefore desired to provide an improved device.